Magnesium has large electric capacity per unit volume, because an ion thereof is a polyvalent ion. In addition, magnesium has advantages of having not only higher melting point and safer, as compared with lithium, but also small deviation of resource distribution on the earth, and source amount is abundant and is thus cheap. Therefore, a magnesium ion battery adopting metal magnesium as a negative electrode has been noticed as the next generation battery, to replace a lithium ion battery.
However, in the magnesium ion battery adopting metal magnesium as a negative electrode, a passive film is formed on the electrode surface, by a reaction with an electrolytic solution, caused by high reducing performance of magnesium itself. Thus, it hinders reversible dissolution and deposition of magnesium, which makes a negative electrode reaction difficult.
As an electrolytic solution not forming such a passive film, there has been known an electrolytic solution, where a Grignard reagent, RMgX, (wherein R is an alkyl group or an aryl group and X is chlorine or bromine) is dissolved in tetrahydrofuran, where reversible dissolution and deposition of magnesium has been confirmed.
On the other hand, Aurbach et al. have reported that a THF solution of Mg(AlCl2BuEt)2 was prepared, using dibutyl magnesium, Bu2Mg, and ethylaluminum dichloride, EtAlCl2, and it can be used up to potential of about 2.4 V, relative to magnesium (NON-PATENT LITERATURE 1).
However, because these electrolytic solutions using the Grignard reagent or alkylmagnesium have nucleophilic property, there is concern of a direct reaction with an active material having high chemical activity or sulfur, which is used at the positive electrode, therefore, there has been limitation in use as a practical battery.
On the other hand, Wang et al. have reported an electrolytic solution which can be used up to about 2.6 V, relative to magnesium, by mixing a non-nucleophilic phenoxide-type magnesium salt and aluminum chloride (NON-PATENT LITERATURE 2).
In addition, Liao et al. have reported an oxidation resistant electrolytic solution of about 2.5 V, relative to magnesium, by mixing a non-nucleophilic alkoxide-type magnesium salt and aluminum chloride (NON-PATENT LITERATURE 3).